Abstract
Presplit blasting can reduce vibration and back impact induced by cast blasting, thus resulting in a smooth bench slope. To design reasonable presplit blasting parameters, this research investigated the formation of presplit faces based on the explosion mechanics and revealed the cracking mechanism of presplit blasting. According to the stress distribution in the vicinity of the blast holes under the action of explosive stress waves and blasting gas, we deduced theoretical formulae for parameters including charge mass in blast holes, hole spacing, and distance from presplit blast holes to cushion holes. On this basis, a method was proposed for the design of large‐diameter deep‐hole presplit blasting. Field testing was conducted by setting different spacing for presplit blast holes, to monitor the blasting‐induced vibration. The results showed that appropriate hole spacing can reduce the particle vibration velocity and the attenuation index of blasting‐induced vibration changed slightly while the attenuation coefficient decreased significantly; the formed presplit faces were smooth and had a high half‐cast factor. Finally, the reasonable hole spacing for presplit blasting, distance from presplit blast hole to the cushion hole, and the charge mass in blast holes in the Heidaigou open‐pit coal mine were determined, respectively.
Highlights
Presplit blasting is a controlled blasting technology setting dense blast holes along the excavation boundary which are detonated before blasting of primary blast holes, so as to form presplit cracks between the blast area and the reserved area
Based on the Holmquist–Johnson–Cook model, Hu et al built a dynamic damage model of presplit blasting and studied the evolution and formation process of the presplit cracks using numerical simulation [12]. rough numerical simulation, Cai et al reproduced the shattering induced by dynamic impact, propagation, and superposition of stress waves and crack growth driven by blasting gas in a deep-hole presplit blasting process [13, 14]
If the spacing between blast holes is large, it is difficult to form smooth presplit faces; on the contrary, the number of presplit blast holes needs to be increased, which results in a high drilling cost
Summary
Presplit blasting is a controlled blasting technology setting dense blast holes along the excavation boundary which are detonated before blasting of primary blast holes, so as to form presplit cracks between the blast area and the reserved area. Presplit blasting can decrease blasting-induced disturbance and damage, protect the integrity of the rock mass, and form a smooth excavation face. Owing to these advantages, the technology has been extensively used in numerous projects such as mines, railways, and hydraulic engineering works [3]. In terms of cracking mechanism, some scholars believed that the formation of presplit cracks is mainly as a result of the superposition of stress waves due to the simultaneous detonation of adjacent blast holes. Rough numerical simulation, Cai et al reproduced the shattering induced by dynamic impact, propagation, and superposition of stress waves and crack growth driven by blasting gas in a deep-hole presplit blasting process [13, 14]. Field test was carried out to optimise and ascertain the parameters and analyse the vibration-isolation effect of presplit blasting
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